Periodic Reporting for period 1 - QOMUNE (Quantum Optical MUltidimensional NEtworks)
Período documentado: 2023-09-01 hasta 2026-02-28
Quantum Internet will allow unprecedented applications that will dramatically change our lives, spanning from quantum secured communications to distributed quantum simulations, i.e. ultra-precise clock synchronisation, quantum secured identification, efficient distribution of data and energy, quantum sensors and secure access to quantum devices in the cloud.
The main technical limitations currently restricting the range of applicability of the quantum internet are the intrinsic rate-distance limit and the extremely difficult coexistence with the present classical telecommunication infrastructure. Present quantum communication systems mainly use a two-dimensional encoding scheme (qubit) as information unit, which is very fragile and susceptible to external noise. In fact, due to decoherence processes, caused by the interaction with the external environment, the ability of the adopted qubits to remain in superposition and/or in an entangled state is severely jeopardised. On the contrary, by adopting multidimensional quantum states (qudit), which are by nature more robust to noise owing to their higher information efficiency, the potential to realise the quantum internet is within our grasp.
QOMUNE intends to build and test the constituents for a Quantum Internet based on multidimensional quantum states, by combining new technological advances with unconventional quantum interference. QOMUNE envisages a novel scheme for the generation, transmission and interference of qudits, which are fundamental actions of a quantum network. Photonic integrated quantum sources combined with multicore deployed fibres and pioneering design of efficient and scalable multidimensional quantum interference will be adopted for the realisation of QOMUNE building blocks. QOMUNE’s objectives and results will redefine the state-of-the-art of Quantum Internet in terms of tolerance to noise in a realistic scenario and coexistence with the worldwide telecommunication infrastructure.
The main technical limitations currently restricting the range of applicability of the quantum internet are the intrinsic rate-distance limit and the extremely difficult coexistence with the present classical telecommunication infrastructure. Present quantum communication systems mainly use a two-dimensional encoding scheme (qubit) as information unit, which is very fragile and susceptible to external noise. In fact, due to decoherence processes, caused by the interaction with the external environment, the ability of the adopted qubits to remain in superposition and/or in an entangled state is severely jeopardised. On the contrary, by adopting multidimensional quantum states (qudit), which are by nature more robust to noise owing to their higher information efficiency, the potential to realise the quantum internet is within our grasp.
QOMUNE intends to build and test the constituents for a Quantum Internet based on multidimensional quantum states, by combining new technological advances with unconventional quantum interference. QOMUNE envisages a novel scheme for the generation, transmission and interference of qudits, which are fundamental actions of a quantum network. Photonic integrated quantum sources combined with multicore deployed fibres and pioneering design of efficient and scalable multidimensional quantum interference will be adopted for the realisation of QOMUNE building blocks. QOMUNE’s objectives and results will redefine the state-of-the-art of Quantum Internet in terms of tolerance to noise in a realistic scenario and coexistence with the worldwide telecommunication infrastructure.
Development of a novel high-dimensional quantum squeezer
One of the project’s key outcomes is the theoretical design of a squeezer architecture tailored for high-dimensional quantum communication. Squeezed states are fundamental resources in quantum optics, enabling sensitivities beyond the shot-noise limit and supporting secure quantum information processing. Although experimental generation of such squeezed states in qudit or multidimensional protocols was not yet performed within QOMUNE, we developed a detailed theoretical model and performance analysis demonstrating that a compact, stable, and integrated squeezer can be made compatible with quantum photonic platforms. This work defines the required specifications and practical implementation pathways, establishing a clear roadmap toward future experimental realization and integration into multidimensional quantum networks.
Novel scheme for qudit interference via nonlinear optics
QOMUNE introduced a scalable theoretical framework for qudit interference that is independent of the specific degree of freedom employed. The proposed approach exploits nonlinear optical effects—both second- and third-order nonlinearities—to enable controlled interference between qudits of arbitrary dimensionality. This represents a significant step toward realizing complex, high-dimensional quantum operations in integrated photonic systems and provides a versatile foundation for future quantum communication and computation protocols.
Ultra-low-loss integrated photonic chip for quantum optics
A major achievement of the project is the design, fabrication, and experimental validation of an ultra-low-loss integrated photonic chip, developed in collaboration with an external foundry. The device implements a delay-line Mach–Zehnder interferometer, a fundamental component in many quantum photonics experiments. Integrated photonic platforms typically exhibit higher losses than fiber-based systems; our results overcame this limitation, achieving ultra-low optical loss, high interference visibility, and stable performance over extended measurement periods. This development demonstrates the feasibility of robust and scalable integrated photonic platforms for quantum communication experiments, including quantum key distribution (QKD).
Quantum key distribution over multicore fibers (MCF)
While most quantum communication experiments rely on standard single-mode fibers, the optical communications industry is transitioning toward high-bandwidth multicore fibers (MCF). QOMUNE successfully demonstrated QKD using qudits transmitted through deployed MCF infrastructure in the city of L’Aquila, Italy. The experiments confirmed the advantages of qudits over qubits in terms of key generation rate and resilience to losses. In addition, we studied the co-propagation of quantum and classical light in the same MCF, identifying optimal parameters for simultaneous transmission in the C-band. These findings pave the way for the practical integration of quantum and classical channels within next-generation optical networks.
One of the project’s key outcomes is the theoretical design of a squeezer architecture tailored for high-dimensional quantum communication. Squeezed states are fundamental resources in quantum optics, enabling sensitivities beyond the shot-noise limit and supporting secure quantum information processing. Although experimental generation of such squeezed states in qudit or multidimensional protocols was not yet performed within QOMUNE, we developed a detailed theoretical model and performance analysis demonstrating that a compact, stable, and integrated squeezer can be made compatible with quantum photonic platforms. This work defines the required specifications and practical implementation pathways, establishing a clear roadmap toward future experimental realization and integration into multidimensional quantum networks.
Novel scheme for qudit interference via nonlinear optics
QOMUNE introduced a scalable theoretical framework for qudit interference that is independent of the specific degree of freedom employed. The proposed approach exploits nonlinear optical effects—both second- and third-order nonlinearities—to enable controlled interference between qudits of arbitrary dimensionality. This represents a significant step toward realizing complex, high-dimensional quantum operations in integrated photonic systems and provides a versatile foundation for future quantum communication and computation protocols.
Ultra-low-loss integrated photonic chip for quantum optics
A major achievement of the project is the design, fabrication, and experimental validation of an ultra-low-loss integrated photonic chip, developed in collaboration with an external foundry. The device implements a delay-line Mach–Zehnder interferometer, a fundamental component in many quantum photonics experiments. Integrated photonic platforms typically exhibit higher losses than fiber-based systems; our results overcame this limitation, achieving ultra-low optical loss, high interference visibility, and stable performance over extended measurement periods. This development demonstrates the feasibility of robust and scalable integrated photonic platforms for quantum communication experiments, including quantum key distribution (QKD).
Quantum key distribution over multicore fibers (MCF)
While most quantum communication experiments rely on standard single-mode fibers, the optical communications industry is transitioning toward high-bandwidth multicore fibers (MCF). QOMUNE successfully demonstrated QKD using qudits transmitted through deployed MCF infrastructure in the city of L’Aquila, Italy. The experiments confirmed the advantages of qudits over qubits in terms of key generation rate and resilience to losses. In addition, we studied the co-propagation of quantum and classical light in the same MCF, identifying optimal parameters for simultaneous transmission in the C-band. These findings pave the way for the practical integration of quantum and classical channels within next-generation optical networks.
1. The design of a scalable, experimentally implementable, and degree-of-freedom–independent scheme for multidimensional quantum state interference constitutes a major breakthrough. Until now, both theoretical and experimental approaches lacked a viable and practical solution to this challenge. Our results demonstrate that qudits can enhance the performance of quantum systems by increasing information capacity and robustness against losses. This has important implications not only for point-to-point quantum links but also for the more demanding architecture of complex quantum networks. The fact that we have outlined a concrete experimental pathway where previously only theoretical conjectures existed marks a substantial step forward for the field of quantum information science.
2. Photonic circuits are widely regarded as the cornerstone for scaling quantum technologies. Although progress in this area has been rapid, it remains strongly dependent on fabrication processes that are complex and difficult to control. Our demonstration of the integration of a mature telecommunication material into quantum photonic devices provided an elegant and practical solution to this bottleneck. Meeting the stringent requirements of compactness, stability, ultra-low losses, and polarization independence was a significant technical challenge. The iterative design and successful realization of these devices not only advanced our technical expertise but also opened the way toward reproducible, industry-compatible quantum photonic chips. This achievement goes beyond incremental improvement, linking the quantum domain with materials and methods already established in large-scale telecommunications.
3. The demonstration of ququart transmission over a deployed multicore fiber represents the longest-distance transfer of a multidimensional quantum state achieved to date. By employing hybrid encoding—combining time and path degrees of freedom—we developed a scalable platform for qudit generation, transmission, and detection. This result has been widely recognized by the research community, as evidenced by its exceptionally high citation count (57 citations in less than two years). It now serves as a benchmark for future developments in high-dimensional quantum communication.
2. Photonic circuits are widely regarded as the cornerstone for scaling quantum technologies. Although progress in this area has been rapid, it remains strongly dependent on fabrication processes that are complex and difficult to control. Our demonstration of the integration of a mature telecommunication material into quantum photonic devices provided an elegant and practical solution to this bottleneck. Meeting the stringent requirements of compactness, stability, ultra-low losses, and polarization independence was a significant technical challenge. The iterative design and successful realization of these devices not only advanced our technical expertise but also opened the way toward reproducible, industry-compatible quantum photonic chips. This achievement goes beyond incremental improvement, linking the quantum domain with materials and methods already established in large-scale telecommunications.
3. The demonstration of ququart transmission over a deployed multicore fiber represents the longest-distance transfer of a multidimensional quantum state achieved to date. By employing hybrid encoding—combining time and path degrees of freedom—we developed a scalable platform for qudit generation, transmission, and detection. This result has been widely recognized by the research community, as evidenced by its exceptionally high citation count (57 citations in less than two years). It now serves as a benchmark for future developments in high-dimensional quantum communication.